1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to a supporting structure for a granulate hopper on the injection unit of an injection molding machine by means of which the hopper can be selectively attached to a horizontally oriented injection unit and a vertically oriented injection unit.
2. Description of the Prior Art
When the normally horizontally oriented injection unit of an injection molding machine is to be oriented for vertical injection, the hopper which feeds raw material to its plastification cylinder must be reoriented so as to be vertical, or near vertical, for a reliable gravity-flow of the granulate into the injection unit. In order to accomplish this result, it has previously been suggested to arrange the charge chute which leads into the plastification cylinder at an angle of 45 degrees and to attach to it an asymmetrical hopper whose outlet opening is likewise inclined at 45 degrees. By rotating the hopper at its connection to the charge chute 180 degrees, it is possible to obtain a configuration for horizontal injection in which the hopper axis is perpendicular to the injection axis and a configuration for vertical injection in which the hopper axis is parallel to the injection axis. Such a structure is suggested in German Pat. No. 11 50 192.
A different solution is suggested in the German Auslegeschrift (Publ. Allowed Application) No. 28 34 203 and in the corresponding U.S. Pat. No. 4,266,694. They disclose a hopper mounting structure with a mounting hub on the injection unit with an inwardly diverging channel opening and an inclined mounting face, so that it becomes possible, with the aid of two rotatable connectors with oblique end faces, to create, for horizontal injection, a flow channel which is perpendicular to the injection axis and, for vertical injection, a flow channel which is inclined at 45 degrees. The raw material hopper is again asymmetrical, having an inclined outlet. This mounting structure makes it possible to obtain a straight vertical flow direction in the horizontal orientation of the injection unit and a 45-degree inclined flow direction in the vertical orientation of the injection unit.
A major shortcoming of these prior art hopper arrangements is their need for an asymmetrical hopper assembly whose center of gravity is offset from the hopper supporting structure, so that the latter is subjected to stress and fatigue from the weight of the hopper contents. This condition limits the hopper capacity. The lack of symmetry of the hopper itself also precludes the use of a rotary granulate agitator inside the hopper. The latter may be necessary for poorly flowing types of plastic granulate.
Still another possibility of a vertical injection configuration is suggested in the German Offenlegungsschrift (Publ. Application) No. 29 20 584 and in the corresponding U.S. Pat. No. 4,251,204. The arrangement suggested in these publications involves the use of a horizontal connecting cylinder with a driven feeding device.